Answer 504, not 408, when a request outlasts its time limit (closes #70)

The hand-written time limit middleware answered 408 and wrote that
answer from its own goroutine while the handler could still be writing.
It is replaced by chi's middleware.Timeout, placed after
JSONResponseMiddleware so its 504 is not lost behind a 200.

When a handler's database read or other lookup fails, it asks
deadlinePassed whether the request's time limit passed and, if so,
answers 504 instead of its 500 or 404. JSONValidationMiddleware answers
504 with the JSON error body when the limit has passed and the handler
wrote nothing. status.json and /api/v1/stats answer 504 when their
4-second database read runs out.

Model: opus-5-5

internal/server/handlers_test.go

@@ -200,6 +200,179 @@ func TestPrefixDetailHandlersParsePrefix(t *testing.T) {
 	}
 }
 
+// shortRequestDeadline is the deadline the tests below give a request. The
+// server's 30-second limit and the stats handlers' 4-second limit inherit it,
+// so the tests do not wait for either.
+const shortRequestDeadline = 50 * time.Millisecond
+
+// TestRequestPastTimeLimitAnswers504 sends a request through the server's
+// router to a page and to a JSON route whose handlers wait for the time limit
+// to pass and return without answering. The page answers 504; the JSON route
+// answers 504 with the JSON error body. Before the fix both answered 408,
+// written by the time limit middleware from its own goroutine while the
+// handler could still be writing.
+func TestRequestPastTimeLimitAnswers504(t *testing.T) {
+	s := New(nil, streamer.New(logger.New(), metrics.New()), logger.New(), &config.Config{})
+
+	waitForTimeLimit := func(_ http.ResponseWriter, r *http.Request) {
+		<-r.Context().Done()
+	}
+	// Registered the way setupRoutes registers pages and JSON routes.
+	s.router.Get("/slow-page", waitForTimeLimit)
+	s.router.Get("/slow.json", JSONValidationMiddleware(http.HandlerFunc(waitForTimeLimit)).ServeHTTP)
+
+	tests := []struct {
+		path         string
+		wantJSONBody bool
+	}{
+		{path: "/slow-page"},
+		{path: "/slow.json", wantJSONBody: true},
+	}
+
+	for _, tt := range tests {
+		ctx, cancel := context.WithTimeout(context.Background(), shortRequestDeadline)
+		rec := httptest.NewRecorder()
+		s.router.ServeHTTP(rec, httptest.NewRequest(http.MethodGet, tt.path, nil).WithContext(ctx))
+		cancel()
+
+		if rec.Code != http.StatusGatewayTimeout {
+			t.Errorf("%s: status %d, want %d; body %s", tt.path, rec.Code, http.StatusGatewayTimeout, rec.Body)
+		}
+		if tt.wantJSONBody {
+			checkJSONErrorCode(t, tt.path, rec, http.StatusGatewayTimeout)
+		}
+	}
+}
+
+// TestStatsHandlersAnswer504WhenDatabaseReadRunsOut calls each stats handler
+// with a store that does not answer before the handler's 4-second limit runs
+// out, and checks that the handler itself answers 504 with the JSON error
+// body. Before the fix status.json answered 408, and /api/v1/stats wrote
+// nothing, which the JSON check on its route turned into 500.
+func TestStatsHandlersAnswer504WhenDatabaseReadRunsOut(t *testing.T) {
+	release := make(chan struct{})
+	defer close(release)
+	db := blockingStatsDB{release: release}
+	s := New(db, streamer.New(logger.New(), metrics.New()), logger.New(), &config.Config{})
+
+	handlers := map[string]http.HandlerFunc{
+		"status.json": s.handleStatusJSON(),
+		"stats":       s.handleStats(),
+	}
+
+	for name, handler := range handlers {
+		ctx, cancel := context.WithTimeout(context.Background(), shortRequestDeadline)
+		rec := httptest.NewRecorder()
+		handler(rec, httptest.NewRequest(http.MethodGet, "/", nil).WithContext(ctx))
+		cancel()
+
+		if rec.Code != http.StatusGatewayTimeout {
+			t.Errorf("%s: status %d, want %d; body %s", name, rec.Code, http.StatusGatewayTimeout, rec.Body)
+		}
+		checkJSONErrorCode(t, name, rec, http.StatusGatewayTimeout)
+	}
+}
+
+// slowDB embeds database.Store (left nil) and overrides the reads the routes
+// in TestRoutesAnswer504WhenDatabaseReadIsCutOff make. Each read waits until
+// its context ends and returns the context's error, as a slow database read
+// cut off by a time limit does.
+type slowDB struct {
+	database.Store
+}
+
+func (slowDB) GetStatsContext(ctx context.Context) (database.Stats, error) {
+	<-ctx.Done()
+
+	return database.Stats{}, ctx.Err()
+}
+
+func (slowDB) GetIPInfoContext(ctx context.Context, _ string) (*database.IPInfo, error) {
+	<-ctx.Done()
+
+	return nil, ctx.Err()
+}
+
+func (slowDB) GetASDetailsContext(ctx context.Context, _ int) (*database.ASN, []database.LiveRoute, error) {
+	<-ctx.Done()
+
+	return nil, nil, ctx.Err()
+}
+
+func (slowDB) GetPrefixDetailsContext(ctx context.Context, _ string) ([]database.LiveRoute, error) {
+	<-ctx.Done()
+
+	return nil, ctx.Err()
+}
+
+func (slowDB) GetRandomPrefixesByLengthContext(ctx context.Context, _, _, _ int) ([]database.LiveRoute, error) {
+	<-ctx.Done()
+
+	return nil, ctx.Err()
+}
+
+// TestRoutesAnswer504WhenDatabaseReadIsCutOff sends a request through the
+// server's router for each route that reads the database, with a store whose
+// reads fail when the request's time limit passes. Each route answers 504, the
+// JSON routes with the JSON error body. Before the fix they answered 408 or,
+// when the handler wrote first, its own error: 500, or 404 on the IP lookups.
+// The health check is left out: it answers 503 when its own 2-second ping runs
+// out.
+func TestRoutesAnswer504WhenDatabaseReadIsCutOff(t *testing.T) {
+	s := New(slowDB{}, streamer.New(logger.New(), metrics.New()), logger.New(), &config.Config{})
+
+	tests := []struct {
+		path         string
+		wantJSONBody bool
+	}{
+		{path: "/as/64500"},
+		{path: "/prefix/192.0.2.0/24"},
+		{path: "/prefixlength/24"},
+		{path: "/prefixlength6/48"},
+		{path: "/status.json", wantJSONBody: true},
+		{path: "/ip/192.0.2.1", wantJSONBody: true},
+		{path: "/api/v1/stats", wantJSONBody: true},
+		{path: "/api/v1/ip/192.0.2.1", wantJSONBody: true},
+		{path: "/api/v1/as/64500", wantJSONBody: true},
+		{path: "/api/v1/prefix/192.0.2.0/24", wantJSONBody: true},
+	}
+
+	for _, tt := range tests {
+		ctx, cancel := context.WithTimeout(context.Background(), shortRequestDeadline)
+		rec := httptest.NewRecorder()
+		s.router.ServeHTTP(rec, httptest.NewRequest(http.MethodGet, tt.path, nil).WithContext(ctx))
+		cancel()
+
+		if rec.Code != http.StatusGatewayTimeout {
+			t.Errorf("%s: status %d, want %d; body %s", tt.path, rec.Code, http.StatusGatewayTimeout, rec.Body)
+		}
+		if tt.wantJSONBody {
+			checkJSONErrorCode(t, tt.path, rec, http.StatusGatewayTimeout)
+		}
+	}
+}
+
+// checkJSONErrorCode checks that rec holds the JSON error body with the given
+// code.
+func checkJSONErrorCode(t *testing.T, name string, rec *httptest.ResponseRecorder, want int) {
+	t.Helper()
+
+	var body struct {
+		Status string `json:"status"`
+		Error  struct {
+			Code int `json:"code"`
+		} `json:"error"`
+	}
+	if err := json.Unmarshal(rec.Body.Bytes(), &body); err != nil {
+		t.Errorf("%s: decoding the answer %q: %v", name, rec.Body, err)
+
+		return
+	}
+	if body.Status != "error" || body.Error.Code != want {
+		t.Errorf("%s: answer %s, want status \"error\" and error code %d", name, rec.Body, want)
+	}
+}
+
 // settledGoroutineCount lets transient goroutines finish, then reports the
 // current count.
 func settledGoroutineCount() int {